This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We have made a mutant Brome mosaic virus (BMV) that has an interesting biological property. The mutations increase the positive charges inside the viral particles through the addition of two alpha-helices in the N-terminal arginine-rich arm in the capsid subunit of BMV. The X-ray crystal structure of the protein shell of BMV has been solved, but there is no information on the inner layer of RNA and how the N-terminal arm interacts with the RNA. We propose a collaboration where we can use cryo-EM to image and reconstruct the wild-type and mutant BMV. We will then trace the N-terminal arm of the two particles and identify how it interacts with RNA. The goal of this project is to visualize this N-terminal arm that is critical for interaction with the packaged viral RNAs and the structure of the RNAs inside the virion.